Oil-based drilling fluids are widely applied owing to advantages including high well wall stability, stable drilling fluid properties, and oil reservoir protection, because they can fully inhibit hydration of clay minerals in strata. However, oil-based drilling fluids have shortcomings, for example, they may cause severe environmental pollution that is difficult to handle, and have high cost, etc. Hence, presently, developing water-based drilling fluids that attain effects equivalent to those of oil-based drilling fluids as substitutes for oil-based drilling fluids is a trend in the technological development of drilling fluids, especially in shale gas exploitation. Shale strata have a high content of clay minerals, and horizontal shale gas wells have a long horizontal section, resulting in increased time of contact between the drilling fluid and the strata, more severe shale hydration, and more severe well wall instability. To realize the substitution, first of all, water-based drilling fluids must be capable of fully inhibit osmotic hydration and surface hydration of clay minerals just like oil-based drilling fluids. With the present theory and techniques of water-based drilling fluids, only osmotic hydration of clay minerals can be inhibited effectively, but surface hydration of clay minerals can't be inhibited satisfactorily.
Therefore, it is urgent task to make research on and develop a theory and methods for water-based drilling fluids to inhibit surface hydration of clay minerals, in order to create an innovative water-based drilling fluid system that has inhibition capability comparable to that of oil-based drilling fluid systems, has little or no harm to the environment, and can be produced at a low cost, so as to substitute oil-based drilling fluids.